Japanese Laid-Open Patent Publication No. 2007-258541 describes a wiring substrate incorporating electronic components such as chip capacitors. A wiring substrate includes a substrate core including a through hole. The through hole of the substrate core receives an electronic component. To manufacture the wiring substrate, a substrate core including a through hole that is larger than the electronic component is first prepared. A tape is first temporarily fastened to one side of the substrate core in order to seal the through hole. The electronic component is arranged in the through hole from the side that is not sealed by the tape. Under this situation, an insulation layer is formed on the surface of the substrate core that is free from the tape to fix the electronic components. Then, the tape is removed from the substrate core.